I have a question on polyurethane and sheen levels. I have a staining project that I am going to finish with polyurethane. (Minwax gel stain on birch). So I tested three different sheens on a stained sample piece (Minwax fast drying polurethane Satin, Semi-gloss, and Gloss).

I lightly sanded between coats on my sample piece with 400 or 600 grit sandpaper to remove bubbles and increase adhesion. After the last coat, there was still bubbles and imperfections. So I spot sanded with an extra fine sanding sponge. It worked to remove the imperfections, but then the sheen was uneven. Any place that was sanded was substantially less glossy than the unsanded areas. So I decided to keep sanding until it was even and I found that I had sanded off all the sheen of all three samples of polyurethane. In fact - I couldn't tell the difference between the three samples of polyurethane when I was done. At first I thought I sanded off 4 coats of polyurethane with an extra fine sanding sponge, but touching it made me realize it was a very smooth hard surface still in place. In fact, I think I liked the zero sheen look the best. It looks like there is nothing on the wood and is nice and smooth.

So here are my questions for you experts out there.

1. Is it okay to sand off all the sheen on polyurethane? Does it still protect just as well from scratching and moisture? It doesn't look like its even there, I can only feel it.
2. If it is okay, does it matter which polyurethane sheen to use? Satin, Semi-gloss, and gloss?
3. If it is not okay, can I just wipe on a final coat of "wipe on poly" and get full protection of the built up polyurethane but a bubble-less finish as well?